With increasing development of science and technology, a variety of power supply apparatuses or electronic devices are developed toward minimization, high integration and high power. As known, the natural convection is insufficient to remove the heat that is generated by the electronic components. If the heat fails to be effectively dissipated away, the elevated operating temperature may result in damage, reduced use life or deteriorated performance of the electronic components. For effectively removing the heat, the power supply apparatus or the electronic device should be equipped with a forced convection mechanism to exhaust the heat to the ambient air.
Conventionally, the forced convection mechanism of the power supply apparatus or the electronic device uses one or more fan units to drive airflow. For example, plural fan units are arranged side by side and accommodated within the casing of the power supply apparatus to drive the airflow in order to exhaust the heat to the ambient air. Generally, the conventional fan assembly comprises plural fan units and plural backflow prevention units corresponding to respective fan units. In a case that a fan unit is normally operated, plural shutter plates of a corresponding backflow prevention unit are rotated to a first position. Meanwhile, the airflow channel of the backflow prevention unit is opened, and the heat is exhausted to the ambient air through the airflow channel. Whereas, in a case that the fan unit is disabled or has a breakdown, the plural shutter plates of the corresponding backflow prevention unit are rotated to a second position. Meanwhile, the airflow channel of the backflow prevention unit is closed to prevent backflow. In such way, the drawbacks resulting from the backflow (e.g. low flow rate of the airflow within the casing, low heat-dissipating efficiency, etc.) will be solved.
Moreover, the conventional backflow prevention units are usually classified into two types, i.e. an active backflow prevention unit and a passive backflow prevention unit. The active backflow prevention unit uses a flow rate detector and a controller to automatically control the open/close statuses of plural shutter plates of the backflow prevention unit. According to the enabling/disabling status of the corresponding fan unit, the airflow channel of the corresponding backflow prevention unit is opened or closed. The passive backflow prevention unit uses gravity forces of the shutter plates (or springs) and the airflow pressure exerted on the shutter plates to control the open/close statuses of the shutter plates of the backflow prevention unit. According to the enabling/disabling status of the corresponding fan unit, the airflow channel of the corresponding backflow prevention unit is opened or closed.
However, since the active backflow prevention unit needs an additional detector and a complicated controlling circuit, the cost and complexity are higher than the passive backflow prevention unit. Moreover, since the passive backflow prevention unit needs plural springs and a position-confining mechanism to open or close the shutter plates, the configurations and cost of the passive backflow prevention unit are still high. Moreover, depending on the system layout, the power supply apparatus or the electronic device may be placed upright or upside down. In a case that the conventional backflow prevention unit is placed upright, the backflow prevention unit is effective to prevent backflow. Whereas, in a case that the conventional backflow prevention unit is placed upside down, the rotations of the shutter plates may be hindered by each other. In addition, since the airflow channel failed to be completely sheltered by the shutter plates when the backflow prevention unit is placed upside down, there is usually an air gap between adjacent shutter plates. Due to the air gap, if the fan unit is disabled or has a breakdown, the airflow channel is not completely closed. Under this circumstance, a short-circulation problem of the airflow occurs, and thus the heat-dissipating efficiency of the overall system is impaired.